Solve the Problem $1000 \mathrm { ft } ^ { 3 }$

Multiple Choice

Solve the problem.
-An office contains $1000 \mathrm { ft } ^ { 3 }$ of air initially free of carbon monoxide. Starting at time $= 0$ , cigarette smoke containing $4 \%$ carbon monoxide is blown into the room at the rate of $0.5 \mathrm { ft } 3 / \mathrm { min }$ . A ceiling fan keeps the air in the room well circulated and the air leaves the room at the same rate of $0.5 \mathrm { ft } ^ { 3 } / \mathrm { min } ^ { \text {. Find } }$ the time when the concentration of carbon monoxide reaches $0.01 \%$ .

A) 5.01 min
B) 6.01 min
C) 8.01 min
D) 7.01 min